Primary:Illinois has a mixed-hybrid primary system. Voters can change parties each year but must declare a party affiliation at the polls. Depending on which party is chosen, the voter will then be counted as registered for that party. Voters may change party affiliation at polls or caucus.

Voter registration: Voters had to register to vote in the primary by February 21. For the general election, the voter registration deadline was October 9. A "grace period" is also available, allowing voter registration until three days before an election.[1][2]

According to the New York Times race ratings in October 2012, six of the 18 districts are considered to be in play. Those are the 8th, 10th, 11th, 12th, 13th, and 17th districts.[3]

The Center for Voting and Democracy (Fairvote) projected that Democrats would win seven districts while Republicans would win two seats. It did not make a projection for the remaining nine districts.[4]

Primary competitiveness

Illinois was tied with Tennessee and Texas for having the 19th most competitive congressional primaries in 2012, with 55.56% of major party primaries having been contested (20 out of 36). The national average was 54.31%.

Eighteen U.S. House incumbents ran for re-election in Illinois in 2012. 8 of those 18 (44.44%) faced a primary challenger. Nationwide, 200 out of the 386 incumbents seeking re-election faced a primary challenger (51.81%).

Partisan breakdown

Heading into the November 6 election, the Republican Party held 11 of the 19 Congressional seats from Illinois. However, the state lost one seat after the 2010 census and elected 18 representatives.

Margin of victory for winners

There were a total of 18 seats up for election in 2012 in Illinois. The following table shows the margin of victory for each district winner, which is calculated by examining the percentage difference between the top-two vote getters. If the race was uncontested, the margin of victory is listed as 100%.

Candidates

Note: Election results were added on election night as races were called. Vote totals were added after official election results had been certified. For more information about Ballotpedia's election coverage plan, click here. If you find any errors in this list, please email: Geoff Pallay.

Impact of redistricting

With the 2011 redistricting, Illinois lost 1 of its current 19 House seats because the state's population failed to grow as fast as in other states.[64]Illinois had 11 Republican congressmen and 8 Democrats after the November 2010 election.[64] The new map, designed by the dominant Democrats, flipped that advantage to 12 Democrats and only 6 Republicans.[64]